Edema is the swelling of soft tissues due to accumulation of interstitial fluid. The fluid is predominantly water, but protein and cell-rich fluid can accumulate if there is infection or lymphatic obstruction. The swelling is the result of the accumulation of excess fluid under the skin in the spaces within the tissues. All tissues of the body are made up of cells and connective tissues that hold the cells together. This connective tissue around the cells is known as the interstitium.
The body's organs have interstitial spaces where fluid can accumulate. An accumulation of fluid in the interstitial air spaces (alveoli) in the lungs occurs in pulmonary edema. In addition, excess fluid sometimes collects in what is called the third space, which includes cavities in the abdomen (abdominal or peritoneal cavity—called “ascites”) or in the chest (lung or pleural cavity—called “pleural effusion”).
Edema results from increased movement of fluid from the intravascular to the interstitial space, or decreased movement of water from the interstitium into the capillaries or lymphatic vessels. Increased movement of fluid from the intravascular to the interstitial space is due to increased capillary permeability that occurs in infections or as the result of toxin or inflammatory damage to the capillary walls. Edema also results from decreased movement of fluid out of the interstitial space into the capillaries or lymphatic vessels due to lack of adequate plasma oncotic pressure as in nephrotic syndrome, protein-losing enteropathy, or starvation. The lymphatic system is responsible for removing protein and white blood cells (along with some water) from the interstitium. Lymphatic obstruction causes these substances to accumulate in the interstitium.
Lymphedema is a highly disabling disease that causes swollen body limbs due to the malfunctioning of the lymphatic system. It can be inherited (primary) or it can be a consequence of cancer treatment (secondary). Moreover, it is widespread in developing countries as a result of filariasis, a disease caused by a parasitic worm infection, transmitted by mosquitoes. Lymphedema affects approximately 140 million people worldwide. Although epidemiologic data are controversial, it is estimated that in the United States around 6.8 million people have developed or have high risk of developing lymphedema. The incidence of lymphedema is estimated to be around 20% for people undergoing invasive cancer surgery, or other invasive surgeries as hip and knee replacement, cellulitis removal and coronary-artery bypass graft.
In normal conditions, lymphatic vessels absorb up to 1.5 liters per day of fluid (lymph) from the peripheral tissues and they bring it back to the blood circulation. If the lymphatic system is damaged, its drainage action is impaired, resulting in the subcutaneous accumulation of fluid in the limbs, and consequent local swelling. The accumulation of stagnant lymph causes in time dermatitis, pain, weight gain, fatigue, tissue fibrosis, loss of mobility, localized immunodeficiency and recurrent infections. Depression often occurs due to the aesthetical impairment.
As of today, lymphedema cannot be cured. However, a series of therapies are commonly performed, based on the combination of decongestion therapy, massages, lymphatic drainage and compression strategies. These treatments do not remove the cause of the problem but aim only at treating the side effects. Indeed, the disease is not cured and the side effects always come back: the patients must undergo lifelong treatments.
One possible solution for lymphedema could be replacing the function of the damaged lymphatic compartment with an implantable medical system. Implantable medical systems suitable for fluid drainage are known per se. For instance, U.S. Pat. No. 8,157,792 describes a wound drainage system for draining fluid from a wound of a patient. The system includes a system that periodically increases and decreases the application of suction at a drain catheter, together with said drain catheter.
WO 2009/096852 describes an implantable drain adapted to move body fluid from one part of the body to another part of the body. The drainage system enables a patient to easily move around while still being attached to the drain. The drainage system comprises a drainage system for pumping body fluid and a connecting tube and is adapted to be implanted inside the body of the patient. The system can pump body fluid from a treatment area to another part of the body where the fluid can be absorbed and transported out from the body in a normal way. The drainage system has a pump comprising a bellow and a motor may be adapted to compress the bellow and move fluid. The motor is advantageously adapted to repeat the compression at suitable time intervals whereby the drainage system is enabled to repeat the sucking and moving of fluid to substantially constantly suck fluid to the other part of the body.
WO 2014/062679 describes a medical system for moving lymphatic fluid. The medical system may include an implantable body having an inlet end region and an outlet end region represented by an implantable tubular member having one or more fluid openings formed therein. The implantable tubular member may be configured to be implanted or partially implanted in or adjacent to the lymphatic system (e.g., within a lymphatic vessel). The lymphedema medical system may also include a pump coupled to the implantable tubular member. A pump member may be positioned between the inlet end region and the outlet end region. The pump member may be configured to draw lymphatic fluid into the implantable body through the inlet end region and transfer lymphatic fluid out from the implantable body through the outlet end region.
Many other medical systems for draining a fluid are known in the art, such as those described in U.S. Pat. Nos. 8,517,973, 5,762,599, 3,810,259, incorporated herein by reference.
Although such systems are suitable for draining fluid from one body area, or body cavity, to another, they would not be able to absorb and transport fluids distributed in an interstitium, as typical of edemas.
Therefore, there is a need for a system which is capable of draining fluid from an extended area and actively pumping it to reach, directly or indirectly, the bloodstream.